THE ASH OF PLANTS. 189 



Stohmann's single experiment led to the similar con- 

 clusion, that maize may dispense with sodium in the 

 earlier stages of its growth, but requires it for a full 

 development. (Henneberg's Jour, far Landwirthschaft, 

 1863, p. 25.) 



Knop, on the other hand, succeeded in bringing the 

 maize plant to full perfection of parts, if not of size, in a 

 solution which was intended and asserted to contain no 

 sodium. {Vs. St., Ill, p. 301.) Nobbe & Siegert came 

 to the same results in similar trials with buckwheat. 

 Vs. St., IV, p. 339.) 



Later trials by Nobbe, Schroder and Erdmann, and by 

 others, confirm the conclusion that sodium may be nearly 

 or altogether dispensed with by plants. 



The buckwheat represented in Plate I vegetated for 3 

 months in solutions as free as possible from sodium, with 

 the exception of VI, in which sodium was substituted 

 for potassium. 



The experiments of Knop, Nobbe, Siegert and others, 

 while they prove that much sodium is not needful to 

 maize and buckwheat, do not, however, satisfactorily 

 demonstrate that a little sodium is not necessary, because 

 the solutions in which the roots of the plants were im- 

 mersed stood for months in glass vessels, and could 

 scarcely fail to dissolve some sodium from the glass. 

 Again, slight impurity of the substances which were em- 

 ployed in making the solution could scarcely be avoided 

 without extraordinary precautions, and, finally, the seeds 

 of these plants might originally have contained enough 

 sodium to supply this substance to the plants in appre- 

 ciable quantity. 



To sum up, it appears from all the facts before us : 



1. That sodium is never totally absent from plants, 

 and that, 



2. If indispensable, but a minute amount of It is 

 requisite. 



